5F2A Weirdness...Troubleshooting

Team, your comments are appreciated. I am reinvigorated and pumped to get back on this.

The only downer is my demanding full time day job is holding me back. Being a part time amp hack I forget more than I’ve learned it seems.

I do have an O-scope. I have played with it a bit. It’s still fairly foreign to me. I also have a signal generator I can pump into the preamp. What I still need it a bigazz 100W wire wound resistor dummy load. Its painful hearing 1,000 hz Wave through the amp. I’d like to dig the scope back out and learn more with it. If ya’ll will guide me through it.

I did use my DMM last night to pick up the milli-volt AC signal from strumming the guitar, at V1 input. It’s there.

1. Burnt my face with my soldering iron. LOL. It can happen!
2. Took 480 volts DC through my right index finger. Off preamp stage. Amp was unplugged. I had drained caps about 40 times before this incident. It only takes once.
3. Walked away, left with a reminder when I look in the mirror...Stupid hurts.

Alright. Wounds licked. Repaired and slammed another amp out this week. No more screwing around. Back to this 5F2A. I took some voltage measurements tonight. See attached schematic. I see something that tweaks me, but I am not sure why I am seeing this symptom.
See pic below:

Alright. Wounds licked. Repaired and slammed another amp out this week. No more screwing around. Back to this 5F2A. I took some voltage measurements tonight. See attached schematic. I see something that tweaks me, but I am not sure why I am seeing this symptom.
See pic below:

That's normal; the tubes are conducting different currents through the plate resistors, due to differences in their characteristics.
Edit: while differences are normal, that's a really large difference, as snfoilhat pointed out.

I looked back through the thread just now. You said you replaced the NFB resistor, that's the 22k from the speaker jack right?

Check the junction of the 22k, 1.5k, and lead from V1 pin 8 very closely. If that joint is compromised, or the 1.5k is toast, that would cause your issues.

I'd lift the NFB lead at the speaker jack and verify that circuit. That lead should measure 23.5k to ground, and V1 pin 8 should be 1.5k to ground.

Since the power tube arced, the cathode capacitor on it may also have been damaged by overvoltage. Clipping a new one in around it, or temporarily replacing it, would also be something I'd try if getting V1b under control doesn't solve this.

Hooked up wrong. Doh. I checked everything so many times. My board is not laid out like the Weber layout in post #10. The 22K NFB resistor into the 1500K resistor, is to the right of the 6V6 cathode cap and resistor. Threw me off, and I was too stubborn to see it. I had the 1500R connected to the turret at the coupling cap to the right of it.

Thanks folks for putting up with a couple of cranky sessions lately. Amp is now better than it was. I rewired it with cloth push-back wire. Reduced voltage now by way of zener diodes.
New resistors. 2 new coupling caps. A 470R 5W grid resistor added. It sounds great.

Humbly knocked back a few pegs, gained more experience and tried a few new things. All in all a good experience.

Hooked up wrong. Doh. I checked everything so many times. My board is not laid out like the Weber layout in post #10. The 22K NFB resistor into the 1500K resistor, is to the right of the 6V6 cathode cap and resistor. Threw me off, and I was too stubborn to see it. I had the 1500R connected to the turret at the coupling cap to the right of it.

Thanks folks for putting up with a couple of cranky sessions lately. Amp is now better than it was. I rewired it with cloth push-back wire. Reduced voltage now by way of zener diodes.
New resistors. 2 new coupling caps. A 470R 5W grid resistor added. It sounds great.

Humbly knocked back a few pegs, gained more experience and tried a few new things. All in all a good experience.